Magnetic recording media for audio equipment, video deck and computer (e.g., disc and memory tape) use commonly include a non-magnetic support having thereon a magnetic layer comprising a ferromagnetic powder dispersed in a binder.
In recent years, there has been a growing demand for high density recording. To this end, the signal/noise ratio (S/N) has been improved by employing finer powders of ferromagnetic materials or powdered ferromagnetic alloys, packing the ferromagnetic powder at a higher density, or extremely smoothing the surface of the magnetic recording medium so that a higher signal level or lower noise level can be obtained. In order to permit high density recording, it is necessary that the time for writing and reading on the magnetic recording medium be shortened. This requires the magnetic recording medium to travel at a high speed. Since the magnetic recording medium needs to be adapted to travel at a high speed, it also needs to exhibit excellent running performance, antistatic property and head cleaning properties. To this end, fillers such as carbon black and abrasive having a Mohs' hardness of 8 or more have been employed. Specific examples of such fillers are disclosed in U.S. Pat. Nos. 3,630,910, 3,833,412, 4,614,685, and 4,539,257, and JP-A-59-193,533 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
However, even with these approaches, it has been extremely difficult to fully satisfy running durability when the tape travels at a high speed. The reason for this problem is that a high S/N can be obtained only by making the magnetic recording medium ultrasmooth which increases the friction coefficient of the magnetic tape.
The inventors have made extensive studies to lower the friction coefficient of an ultrasmooth surface.
In particular, in order to maximize the output from the magnetic tape, it is conventional to orient ferromagnetic particles with their longer axis parallel to the running direction of the tape in the coating surface, and as horizontal as possible in the running direction. While this approach permits an increase in the output and an improvement in the squareness ratio (Br/Bm), it fails to eliminate dropout or improve running durability such as still life. Dropout may be caused by a binder, but is more often caused by a ferromagnetic powder. The inventors have investigated the friction coefficient of ferromagnetic powder and its effect on dropout. As a result, it has now been found that the orientation of the ferromagnetic powder present in the magnetic layer has a great effect on the friction coefficient of ferromagnetic powder and the occurrence of dropout. In order to solve these problems, the orientation of the ferromagnetic powder was studied by a high energy electron ray diffraction method. As a result, it has now been discovered that the orientation of the ferromagnetic powder has a significant relationship to dropout, still life, and squareness ratio (Br/Bm).